1. Field of Invention
The present invention relates to IP networks and in particular to a dynamic admission control (AC) function providing assured Quality of Service (QoS) for an IP network with differentiated services (DiffServ) capabilities.
2. Related Art
Present IP carrier networks provide unreliable best-effort service to their users. Regardless of the application type all packets receive the same treatment. With the expansion of the Internet and the availability of high capacity routing and transmission technology, Internet Service Providers (ISPs) are planning networks capable of providing differentiated services to their customers with QoS assurances in addition to the traditional best-effort service.
Two network architectures have been proposed by the Internet Engineering Task Force (IETF) to support the IP QoS requests. The first architecture allows resource reservation per flow. This is called the Integrated Services (IntServ) architecture and uses a reservation setup protocol (RSVP) as the signalling protocol to pass the QoS requests from the end system to each intermediate router along a data path. An admission control (AC) mechanism at each router along the path verifies the resources needed to provide the requested QoS. If the QoS requirements can be met, resources are reserved on an end-to-end basis, and each router is required to maintain a state for each flow traversing the network.
This architecture is suitable for a small network with a small number of flows to be managed, but becomes a problem in a carrier-scale network, where each router needs to keep states for a large number of flows.
In the second architecture, the complexity is moved to the edges of the network, hence keeping the core simple. This architecture is called the Differentiated Services (DiffServ, or DS) and it uses traffic aggregates instead of maintaining a state for each individual flow at each router. Traffic conditioning is done at the edge of the network as part of the end-to-end service. The routers in a DiffServ network implement a set of well-defined packet forwarding treatment called Per-Hop Behavior (PHB). Each PHB is given a unique default DiffServ code-point (DSCP) in the DiffServ field of the packet header, e.g. type of services (ToS, or service type) bytes in IP version 4, or Traffic Class byte in IP version 6. At the DiffServ network boundary, the routers classify the traffic flows and mark the DiffServ field with the appropriate code-point. Intermediate routers along the path provide different forwarding treatment to the packets according to the code-point in each packet. It is expected that edge routers will only maintain a state record for each individual flow and therefore, scalability is no longer an issue. The DiffServ architecture is preferred as it is easy to implement and scales to a large network.
The ability to differentiate between data packets having different QoS requirements is a necessary, but not sufficient condition for offering assured QoS. For satisfying services with QoS parameters attached to them, traffic management mechanisms are required to ensure that sufficient resources exist to meet the service objectives. Prominent among those mechanisms is the AC function which limits the volume of the traffic accepted to the network to allow the various QoS objectives to be satisfied.
A service request may be a single-ended or a double-ended request. Although both types of requests specify the amount of traffic and the services required, a single-ended request specifies only the traffic origination. A double-ended request specifies the traffic origination and the traffic destination. Both single-ended and double-ended requests need to be supported by an efficient admission control method whenever assured performance is required.
The support of assured QoS in a DiffServ network is not an easy task since there is no a priori knowledge of the path to be followed, particularly for single-ended requests which could be directed to any destination. A basic weakest link method has been suggested for controlling the amount of traffic allowed to enter a network. This method is very inefficient in terms of bandwidth utilization.
Accordingly, there is a need to provide a method and a mechanism for dynamically supporting IP QoS in a DiffServ network, to ensure that QoS requirements are met for admitted data packets, while efficiently utilizing the network.
An object of the invention is to provide admission control mechanisms which alleviate totally or in part the drawbacks of the prior art.
It is another object of the invention to provide a mechanism for a carrier IP network to perform admission control (AC) for service requests with assured QoS. The AC mechanism operates for both single or double ended requests by dynamically deciding whether the request should be accepted or rejected.
Still another object of the present invention is to provide admission control (AC) using an iterative measurement based method for carrier IP networks. A QoS manager keeps track of the resource availability of the network, and accepts a new request only if the requested resource is available. The QoS manager maintains an accurate resource occupancy table using, or supplementing with direct measurements from the network.
According to one aspect of the invention, an iterative weakest link method is provided. The method comprises the steps of initializing a QoS manager at an admit limit (AL) representing a bandwidth utilization capacity allocated to a service offered on the weakest link of the network; receiving a service request including a service type and a required bandwidth; comparing the AL with the required bandwidth and accepting the request whenever the required bandwidth does not exceed the AL, and rejecting the request whenever the required bandwidth exceeds the AL; maintaining the AL if the request is rejected and dynamically adjusting the AL by the amount of required bandwidth after accepting the request, while periodically measuring the traffic load on each link of the network to provide an updated AL for each offered service.
According to another aspect of the invention, a path-based method using the iterative measurement technique with the edge routers supplying the path, is provided. This method comprises the edge routers maintaining a spanning tree, and the QoS manager maintaining the link occupancy table. Edge routers intercept the service request sent by a customer, identify the path the request will use, and forwards the service report together with the assigned path to the QoS manager. The QoS manager accepts or rejects the request based on the service requested, the path required, and the available capacity of the links along the assigned path.
According to still another aspect of the invention, a path-based method using the iterative measurement with the QoS manager maintaining both. the routing table and the link occupancy table, is provided.
The AC process according to the invention advantageously provides support for both single-ended and double-ended service requests, and also provides improved bandwidth utilization.
The invention is not limited to the features disclosed in the xe2x80x9cSummary of the Inventionxe2x80x9d section; it nonetheless may reside in a sub-combination of the disclosed features.